mbrobbel commented on a change in pull request #11937:
URL: https://github.com/apache/arrow/pull/11937#discussion_r771354239
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File path: cpp/src/arrow/compute/api_vector.h
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@@ -188,6 +188,35 @@ class ARROW_EXPORT PartitionNthOptions : public
FunctionOptions {
NullPlacement null_placement;
};
+/// \brief Options for IsMonotonic
+class ARROW_EXPORT IsMonotonicOptions : public FunctionOptions {
+ public:
+ enum NullHandling {
+ /// Ignore nulls.
+ IGNORE_NULLS,
+ /// Use min value of element type as the value of nulls.
+ /// -Inf for floating point numbers.
+ USE_MIN_VALUE,
+ /// Use max value of element type as the value of nulls.
+ /// Inf for floating point numbers.
+ USE_MAX_VALUE
+ };
Review comment:
Yes, I agree that a sort before invoking this kernel should result in
true for the corresponding check. However I feel the null handling variants are
a bit confusing: `AtStart` defines `NaN > null` and `AtEnd` defines `NaN <
null`. Also, the sorting kernel can ignore equality, but this kernels considers
it to check if values are unique (strictly increasing/decreasing).
I think if we want to allow users to define order of unordered values (both
for sorting and this kernel) we need something like this:
```c++
bool compare_nulls = false; // default: any null results in false outputs
(or error in case of sort)
bool compare_nans = false; // default: any nan results in false outputs (or
error in case of sort)
// these are not needed when sorting
bool nulls_equal = false; // when nulls are compared, are they considered
equal?
bool nans_equal = false; // when nans are compared, are they considered
equal?
// when both nulls and nans are compared
enum Ordering { Less, Equal, Greater }
Ordering nan_compared_with_null; // when comparing nulls and nans, what
ordering should be used?
```
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